MILITARY  TOPOGRAPHY 


AND 


MAP  READING 


BY 

CAPT.  W.  H.  WALDRON 

29th  infantry 


Reprinted  from 

"NIGHT  OPERATIONS" 

Infantry  Journal 

July,  1917 


WASHINGTON 

United  States  Infantry  Association 
1917 


Night  Operations 

A  Department  devoted  to  the  interest  of  newly  commissioned  Infantry 
Officers,  Officers  of  the  Infantry  Officers'  Reserve  Corps,  and  candidates  for 
Commission. 

Conducted  by  Capt.  W.  H.  Waldron,  29th  Infantry 


MILITARY    TOPOGRAPHY    AND    MILITARY     MAP 
READING 

For  admission  to  the  Officers'  Reserve 
Corps  or  promotion  to  a  higher  grade  in  that 
corps,  the  provisions  of  General  Orders  No. 
32  require  of  the  candidate  the  making  of  a 
military  topographic  map  (sketch)  and  a 
practical  knowledge  of  map  reading. 

In  the  space  available  for  this  article  it  is 
impracticable  to  provide  a  text  containing 
the  process  of  military  map  (sketch)  mak- 
ing. To  give  you  a  few  hints  that  will  help 
you  over  some  of  the  rough  places  and  to 
inform  you  where  the  detailed  information 
on  subject  may  be  obtained  is  all  that  will 
be  attempted. 

The  United  States  Infantry  Association 
are  the  publishers  and  distributors  of  a  book 
written  by  Capt.  Loren  C.  Grieves,  30th  In- 
fantry, for  the  instruction  of  noncommis- 
sioned officers  of  the  Army  on  the  subjects 
of  Military  Sketching  (which  is,  so  far  as 
you  are  concerned,  the  same  as  topographic 
map  making)  and  Map  Reading.  This  book 
is  written  in  progressive  lesson  form  and 
provides  a  text  from  which  you  will  be  able  to 
master  the  subject  within  a  reasonable  length 
of  time.  The  book  may  be  had  from  the 
United  States  Infantry  Association,  Union 
Trust  Building,  Washington,  D.  C.  The  price 
is  $1.00,  postage  paid.  This  book  is  highly 
recommended  by  the  editor  of  this  de- 
partment. 

The  making  of  a  military  sketch  may  be 
accomplished  in  only  one  way,  and  that  is  to 
"go  out  and  make  it."  You  will  never  gain 
a  mastery  over  the  subject  by  sitting  at  your 
desk  and  studying  the  text-book.  You  will 
have  to  get  out  in  the  country  and  go  through 
the  process,  not  one  but  many  times. 

As  in  any  other  line  of  endeavor  the  first 
requisite  for  success  is  the  possession  of  the 
proper  tools  for  the  work.  If  you  start  out 
with  makeshifts,  you  are  doomed  to  discour- 
agement and  failure. 


1.  You  must  have  a  drawing  board,  upon 
the  surface  of  which  the  paper  on  which 
your  sketch  is  to  be  drawn  may  be  attached. 
The  book  department  of  the  Army  Service 
Schools  at  Fort  Leavenworth,  Kansas,  has 
devised  a  sketching  board  that  has  met  the 
requirements  at  that  institution.  It  has  a 
3H-inch  declinator  and  is  probably  the  best 
that  can  be  produced  for  a  moderate  price. 
The  price  of  this  board  complete  is  $5.50. 
A  folding  head  tripod  for  the  board  costs 
an  additional  $2.75. 

2.  Your  next  requisite  is  a  means  for  at- 
tammg  the  direction  of  one  point  from  an- 
other. This  is  supplied  by  the  alidade  ruler 
upon  the  six  surfaces  of  which  your  scales 
may  be  pasted.  The  book  department  of 
the  Army  Service  Schools  at  Fort  Leaven- 
worth also  supplies  this  instrument  at  a  cost 
of  20  cents  each.  It  is  made  of  seasoned 
wood,  weighted  with,  lead  so  that  it  will  lie 
flat  on  the  surface  of  the  paper  and  not  be 
disturbed  by  wind.  It  is  triangular  shaped 
in  cross-section  and  is  about  6  inches  in 
length. 

3.  You  will  require  some  method  for  de- 
termining the  slope  of  the  ground  at  any 
given  point  and  the  difference  in  elevation 
of  any  two  or  more  points.  This  is  accom- 
plished by  reading  the  vertical  angle.  The 
regular  instrument  designed  for  this  purpose 
is  the  clinometer,  which  is  very  expensive. 
As  a  substitute  we  use  the  slope  board.  On 
pages  43  to  45  of  Captain  Grieves'  book  are 
detailed  instructions  for  laying  oflF  a  slope 
board  on  your  ordinary  sketching  board  de- 
scribed in  paragraph  1  above.  You  will  find 
this  sufficiently  accurate  for  all  practical 
purposes. 

4.  You  will  need  lead  pencils— 4H  and  6H 
are  the  best— a*  soft  rubber  eraser,  thumb 
tacks  and  sketching  paper.  This  latter 
should  be  carefully  selected,  for  you  cannot 
accomplish  the  necessary  "rubbing  out"  on 
inferior  paper. 


374384 


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4  ;•.♦;,•,*„'*«'    iNrig'lit   Operations 

-'oQ*'  :,v';  1,. — ;  ;^,u  ?ao  .,  .' __ 

5.  Finally    you    will    require    a    scale    of  tions  of  all  objects  of  military  impor- 

paces,    which   will    be   considered    in    detail  tance  in  the  area  represented, 

later.    As  a  refinement  I  would  advise  your  Q.  What  is  map  reading? 

procuring  a  canvas  pencil  holder.  A.  T\\q  ability  to  correctly  interpret  a  map 

Now  let  us  see  what  all  of  this  is  going  to  and  to   form  a  mental  picture  of  the 

cost  you :  ground  it  is  intended  to  represent. 

Q.  What  are  the  essential  elements  of  map 

1  sketching  board $5.50  reading? 

1  tripod  for  sketching  board 2.75  a.  1.  The  conversion  of  map  distances  into 

1  alidade    scales    with    stride    and  corresponding   ground    distances;    that 

pace  sheets..., 20  jg^  ^n  appreciation  of  the  scale  of  the 

1  eraser,  soft  rubber 10  map. 

2  pencils,  lead,  4H 15  2.  A     knowledge     of'     the     conventional 

1  roll  paper,  sketching  (20  yds.) ...     .65  signs    and    symbols    employed    by    the 

1  pencil  holder,  canvas 30  map    makers    to    represent    the    topo- 

,  Thumb  tacks,  2  dozen 20  graphical   features   of   the  country   in- 

1  triangle,  ambro,  6  inch  (30  to  60).     .20  eluded  in  the  map. 

1  text-book.   Captain   Grieves' 1.00  ^   An  appreciation  of  direction. 

4.  A    knowledge    of    contours    and    what 

Total  cost $11.05  ^j^gy  ^j-g  intended  to  represent. 

..,,,.                        ,      ,                ,  Q-  What  is  the  scale  of  a  map? 

All  of  these  Items  except  the  last  may  be  ^_  ^^^  ^^^j^  ^^  ^  ^^p  .^  ^^^  ^^^.^  ^^  ^^^ 

procured  by  addressmg  a  letter  to  The  Secre-  ^.^^^^^^    ^^^^^^^    ^^^    p^.^^^    ^^    ^^^ 

tary.  Army   Service   Schools,   tort   Leaven-  j--jju      ^u      u     •       4.ij- 

■'',     ^^  ^           ,      ,           ,         ,  ,        •         ,  map    divided    by    the    horizontal    dis- 

worth    Kansas;  the  latter  by  addressing  the  ^^^^^      ^^^^^^^      ^^^      corresponding 

United   States   In  antry   Association,   Union  ^^.^^^  ^^  ^^^  ^^^^^^^ 

Trust  Buikimg,  Washington,  D.  C.          _  ^    ^^^^  ^^^  ^^^  ^^^^^^  prescribed  for  mili- 

You  will  need  every  one  of  these  articles.  ^^^^  ^^^^^  ^^  ^^^  ^^^.^^, 

To  go  out  without  them  means  unsatisfactory  ^^  ^^  ^j^^^^  j^^^^^  ^q^^^  ^^^  ^jl^^  ^^^  ^^^^ 

work  and  discouragement      This  is  a  good  ^^^^^^^^  ^^^  ^^p^_ 

outfit  and  one  that  you  will  use  m  the  course  ^   gj^  ^^^^^^  ^^^^1  ^^^  ^jl^^  ^^^  p^^j^j^^ 

of   your  instruction  work  in  topography  at  ^^^^^^^^  ^^^  ^^p^_ 

the  summer  training  camps  for  Reserve  Offi-  3   ^^^^^^  .^^^^^^  ^^^^j  ^^^  ^jl^^  ^^^  ^^p^ 

cers.     You   will   find   it   one   of   your   best  ^^^  ^^^^^^^^  ^^  ^^^^^  j^  j^  j^^^^^^^  ^^ 

friends    in    the   prosecution    of    your    work  ^^^^^j^^  defensive  positions, 

there,   and  you  will   find   it  handy   m  your  ^^^   ^^^    ^^^   ^^^^^    ^^   ^  ^^^    ^^    ^^. 

solution  of  tactical  problems  incident  to  the  .^ 

tactical  walks  in  minor  tactics  that  you  will  ^    j_  BTa'plain  statement  in  words  and  fig- 

have,  especially  where  you  have  an  oppor-  ^^^^  ^^  ^^^  ^^j^^^^^  ^^^^^^^  ^^^  ^^p 

tunity  to   mdicate  your  dispositions   by  the  ^.^^^^^^  ^^^  ^^^  ^^^^^^  distance;  for 

means  of  a  rough  sketch.  example."  3   inches  to   1   mile."     This 

In  studying  the  subject,  go  over  each  lesson  ^^^^^  ^^^^  ^^^  3   .^^j^^^  ^^  ^j^^  ^^^ 

as  laid  down  by  Captain  Grieves.    They  have  ,   .              j-      .•          -n   >»..,- 

"    „       ,          ,     ^       1       1       \.      r  measured  in  any  direction  will  reprc- 

been  carefully  planned.    Get  the  elements  of  .  ,      -i          .1                j 

1     r      ,     n     A    ■                   -A      r)^„^f,v»  sent  1  mile  on  the  ground, 

each   firmly   fixed   in   your   mind.     Practice  .    •       r      .•       •        u-  u 

the  making  of  the  conventional  signs  until  2.  By  a  representative  fraction  m  which 

you  do  not  have  to  refei;  to  the  text-book  for  the  enumerator  represents  the  map  dis- 

them.     Get  out  in  the  country  and  actually  tance  and  the  denommator  represents 

make  a  map   in   accordance  with  the  rules  the  ground  distance  in  the  same  unit  of 

laid  down  in  your  text-book.  measure,    thus          \,      would   be   the 

10,560 

MILITARY  MAP  READING  representative  fraction  for  6  inches  to 

Q.  What  is  a  military  map?  1   mile;  that  is,  one  unit  of  measure 

A.  A  military  map  is  one  which  shows  the  on  the  map,  as  1  inch,  would  represent 

relative  distances,  elevations  and  direc-  10,560  inches  on  the  ground.    One  pen- 


Night   Operations 


cil  length  on  the  map  would  represent 
10,560  pencil  lengths  on  the  ground. 

3.  By  a  graphical  scale  in  which  a  line  is 
drawn  on  the  map  and  divided  into 
equal  parts,  the  divisions  being  marked, 
not  with  their  actual  lengths,  but  with 
the  ground  distance  that  they  represent. 

What  are  the  two  classes  of  scales? 

Working  scales  and  reading  scales. 

What  are  working  scales? 

6"to  T  Mile 
Scale  of  paces 


place  the  edge  of  the  paper  along  each 
stretch,  placing  the  point  of  a  pencil 
at  each  successive  point  where  the  di- 
rection changes,  the  paper  may  be 
twisted  around  to  follow  the  bends  of 
the  course  until  the  total  distance  has 
been  covered.  Apply  this  total  distance 
to  the  scale  of  the  map  and  read  direct. 
A  few  trials  at  this  will  perfect  you  in 
the  method. 


8§°S 


88  S  8  88  8 


Scale  of  paces  < 
3"to  1  Mile 


Fig.  1 


A,  Working  scales  are  those  representing 
the  unit  of  measure  with  which  the 
map  was  made;  that  is,  paces,  strides 
of  a  horse,  length  of  a  rope,  etc. 

Q.  What  are  reading  scales? 

A.  Reading  scales  are  those  made  for  laying 
off  distances  on  the  map  and  should 
be  in  some  familiar  unit  of  measure 
such  as  yards  or  feet.  In  some  cases 
the  reading  scale  may  be  identical  with 
the  working  scale  as  where  the  working 
scale  is  paces  of  Z6  inches,  the  corre- 
sponding reading  scale  would  be  yards. 

Q.  How  would  you  determine  the  distance 
between  two  points  on  a  map? 

A.  By  measuring  along  the  edge  of  a  piece 
of  paper  the  distance  between  the  two 
points  under  consideration  and  apply- 
ing th's  distance  to  the  scale  of'  the 
map  and  reading  directly  from  it.  To 
measure  the  distance  from  one  point 
to    another    along    a    winding    course, 


Q.  What  is  a   convenient  formula  for   the 

solution  of  scale  problems? 
A.  Let  w  =  the  number  of  units  of  measure 
to  be  represented  by  the  scale 
line.  In  linear  scales  make 
this  always  2,000,  so  there  is 
nothing  further  to  remember. 

Let  p  =  the  number  of  inches  in  the  unit 
of  measure.  For  a  scale  of 
yards  p  would  be  36,  for  a 
scale  of  30-inch  paces  p  would 
be  30,  for  a  scale  of  meters  p 
would  be  39.37. 

Let  n  =the  denominator  of  the  repre- 
sentative fraction.  For  3 
inches  to  the  mile  n  would  be 
21,120;  for  6  inches  to  the 
mile  n  would  be  10,560,  for  12 
inches  to  the  mile  n  would  be 
5,280. 

Let  .*•  =the  number  of  inches  in  the 
scale  line  to  represent  w 
units  of  measure. 


Night  Operations 


Then 


m  times  p 


For  example :  You  desire  to  con- 
struct a  scale  of  paces  of  30  inches  at 
6  inches  to  1  mile. 

w  =  2,000;  p  =  30;  n  =  10,560. 
2,000  X  30_  ^  _  5_68  inches. 


10,560 

Therefore  a  line  5.68  inches  long  would 
represent  2,000  paces.  Draw  a  line  5.68 
inches  long  and  divide  it  into  five  equal 
parts   of  400  paces   each.     Divide  the 


left   part   into    four   equal   parts    each 
representing  100  paces. 

Except  as  a  means  to  your  under- 
standing of  scales  it  is  not  necessary 
for  you  to  go  to  the  task  of  the  solu- 
tion of  scale  problems.  All  text-books 
on  military  sketching  have  all  the  scales 
that  you  will  ordinarily  use  in  your 
practical  work.  Figure  1  shows  scales 
of  paces  from  27  inches  to  36  inches 
for  3  inches  to  1  mile  6  inches  to  1 
mile.  This  is  all  you  will  ever  have 
any  use  for.  (Taken  from  the  Engi- 
neers' Field  Manual.) 


CONVENTIONAL    SIGNS    AND    SYMBOLS 

Military  Signs. 
I  nf  antry 
In  column    d-d- D- D-D- o 


.niiiiiiiiiiiiiMiDiiiiMin 


DiinitnonrfDprii 
uniif.ifmnoinm 


In  line 


Woods.      Grass  or  meadow.  Cultivated^  Orchard.  =>  •  Rice  swamps 
■                     >  ditch  and  dikes. 


Mud  and         Salt  marsb.       Fresh  marsh         Cypress 
Tidal  Flati  poad.  «wamp. 


Enclosures 

Wire  Fence 

"Barbed 

Smooth 


Cavalry 
Incolur^n    KGBBB& 
In  line  l— i^MHL>Ma« 

Artille^  i,  ii  i   ;^  i   I 

Sentry        (^     Vedette      ^ 

Headquarters  'v?' 


Camp 
Trenches 

Gun 
battery 

Mortar 
battery 


Redoubt 

AAAAAA 

Aaaaaa 


<^o  o^ 


Communications. 


Abattis       '    HfH|^H|^Hf^ 


Chevaux  d« 

frise 


Miscellaneous. 


-t-  -Kr4-  ll°-Kr(-0 


Church 
CecQetB7 


Wind  Milt 


,  Blacksroitfa  Shop 
Wagon  Shop 

Saw  Milt 

Grist  Mill 


Night   Operations 


Q.  How   are    the    features    of    the    country 

represented  on  maps  and  sketches? 
A.  By    means    of    conventional    signs    and 

symbols. 
Q.  What  characteristics  have   these   conven- 
tional signs  and  symbolsf 
A.  They  are  drawn  to  resemble,  as  near  as 
practicable,  the  features  that  they  are 
intended  to  represent. 
There  are  published  herewith  plates  of  the 
ordinary  conventional  signs  and  symbols  em- 
ployed   in    map    and    sketch    making    in    the 
United    States    service.      In    hasty    sketches 
soil  and  cultivation  may  be  indicated  by  sim- 
ply  writing  the  same  in  the  areas  instead  of 
putting  in  the  conventional  signs.  (See  p.  66.) 
You  should  practice  making  these  conven- 
tional signs  until  you  are  familiar  with  them. 
Q.  How  is  the  direction  of  one  point  from 
another  stated  in  military  map  reading  f 
A.  By  the  points  of  the  compass.    One  point 
is  said  to  be  north,  east,  south  or  west 
from  another  point.     When  it  lies  be- 
tween the  north  and  east  points  it  is 
said  to  be  north    (so   many   degrees) 
east;  when  between  the  east  and  south 
it   is    said   to  be   south    (so   many   de- 
grees)   east;   when  between   the   south 
and   west   it   is    said   to   be    south    (so 
many   degrees)    west,   and   when   it   is 
between  the  west  and  north  it  is  said 
to  be  north  (so  many  degrees)  west. 
Q.  How  is  the  north  point  of  a  map  indi- 
cated f 
A.  By  a  line  placed  on  the  map  at  a  con- 
venient place  with  an   arrow   pointing 
to  the  north. 
Q.  Should  a  map  come  into  your  possession 
without    having    the    north    indicated, 
what  conclusion  would  you  draw  as  to 
the  north  point  of  the  map? 
A.  The  sides  of  the  map  generally  run  north 
and  south.     The  lettering  usually  runs 
from  east  to  west.     These  are  pretty 
good  guides. 
Q.  What  do  you  understand  by  orienting  a 

map  ? 
A.  Placing  the  map  in  such  position  that 
every  road,  stream,  or  other  feature 
on  the  map  will  be  parallel  to  its  actual 
position  on  the  ground ;  in  other  words, 
to  make  the  map  and  the  ground  it 
represents  coincide. 
Q.  What  are  the  objects  of  orienting  the 
map? 


A.  To  enable  you  to  pick  out  and  identify 
on  the  ground  all  the  features  shown 
on  the  map. 

Q.  By  what  methods  may  a  map  be  oriented? 

A.  1.  When  the  map  has  a  magnetic  merid- 
ian on  it:  Place  the  north  and  south 
line  of  the  compass  parallel  to  the 
magnetic  meridian  and  turn  the  map 
until  the  north  end  of  the  needle  points 
to  the  north  of  the  circle.  If  the  true 
meridian  only  is  shown  on  the  map 
you  must  know  the  declination  and 
make  allowance  for  it.  If  the  declina- 
tion is  not  more  than  4  or  5  de- 
grees the  orientation  on  the  true  merid- 
ian or  along  the  up  and  down  borders 
of  the  map  will  be  sufficiently  accurate 
for  all  practical  purposes. 
2.  When  you  have  no  compass  or  the 
meridian  is  not  shown  on  the  map :  (a) 
If  you  can  locate  on  the  map  your 
position  on  the  ground  and  can  identify 
another  place  on  the  map  which  you 
can  see  on  the  ground,  shift  the  map 
around  until  the  two  points  on  the 
map  are  aligned  on  the  distant  point 
on  the  ground  and  you  have  the  map 
oriented.  (6)  By  reference  to  a 
straight  road  or  line  of  railway  on 
which  you  may  be  standing  turn  the 
map  until  the  conventional  symbol 
points  in  the  same  direction  as  the  fea- 
ture that  it  represents.  In  both  of  these 
methods  the  points  used  for  orientation 
should  be  as  far  apart  as  possible  and 
in  any  case  they  should  be  more  than 
an  inch  apart  on  the  map. 

Q.  How  would  you  locate  your  position  on 
the  map? 

A.  1.  When  the  map  has  been  oriented  by 
compass.  Sight  along  the  ruler  at  an 
object  on  the  ground  at  the  same  time 
keeping  the  ruler  on  the  plotted  posi- 
tion of  this  same  object  on  the  map. 
Draw  a  line  towards  yourself.  Locate 
another  point  on  the  ground  that  is 
plotted  on  the  map  and  repeat  the 
process.  The  intersection  of  these  two 
lines  is  your  map  position.  These  lines 
should  form  an  angle  of  not  less  than 
30  degrees  and  not  more  than  ISO 
degrees. 
2.  If  the  map  has  been  oriented  by  means 
of  a  straight  line  drawn  between  two 
map  points,  it  will  be  necessary  to  draw 


8 


Night   Operations 


but  one  line  from  an  object  on  the 
ground,  and  the  intersection  of  this 
line  with  the  line  already  on  the  map 
will  be  your  location  on  the  map. 

Q.  What  are   contours? 

A.  They  are  lines  cut  from  the  surface  of 
the  earth  by  imaginary  horizontal 
planes  spaced  at  equal  vertical  inter- 
vals from  each  other, 

Q.  What  do  contours  show? 

A.  1.  The  relative  elevation  of  all  points  on 
the  map. 

2.  The  slope  between  any  two  points  on 
the  map. 

3.  The  shape  and  form  of  the  ground  in- 
cluded within  the  limits  of  the  map. 

Q.  What  general  characteristics  have  con- 
tours? 


is   indicated   by   the   contours   bending 
sharply  towards  the  higher  ones. 

5.  When  two  contours  of  different  eleva- 
tions join  together  and  form  one  line 
they  indicate  a  cliff.  Where  a  higher 
one  crosses  a  lower  one  it  is  an  over- 
hanging cliff. 

6.  A  saddle  or  col  is  the  space  between 
the  summits  of  two  adjacent  hills.  It 
is  indicated  by  two  contours  of  greater 
elevation  on  two  sides  of  it  and  two 
contours  of  less  elevation  on  the  other 
two  sides. 

Q.  What   do   you  understand   by    the    term 

"horizontal  equivalent?" 
A.  It  is  the  horizontal  distance  on  the  ground 

between  two  contours. 
Q.  What  is  a  scale  of  horizontal  equivalents? 


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Fig.  2. — Scale  of  Horizontal  Equivalents. 


A.  1.  All  contours  join  or  extend  to  the 
edge  of  the  map.  When  they  join  they 
either  represent  a  hill  top  or  a  depres- 
sion— a  hill  when  the  smallest  closed 
contour  is  higher  than  the  adjoining 
one  and  a  depression  when  it  is  lower. 

2.  Where  the  contours  are  equally  spaced 
the  slope  is  uniform.  Where  they  are 
wide  apart  the  slope  is  gradual  and 
where  they  are  close  together  it  is 
steep. 

3.  A  watershed  is  the  high  ground  be- 
tween two  watercourses.  The  water 
flows  away  from  it  on  both  sides  and 
is  indicated  by  the  higher  contours 
bulging  out  towards  the  lower  ones. 

4.  A  watercourse  is  the  low  ground  be- 
tween two  watersheds.  The  rain  from 
both  sides  of  it  join  in  one  stream  and 


A.  1.  The  scale  of  horizontal  equivalents  is 
based  on  the  fact  that  at  a  slope  of  one 
degree  the  ground  will  gain  an  eleva- 
tion of  1  foot  in  57.3  feet. 

2.  Thus  where  a  vertical  interval  of  10 
feet  is  being  used  this  10  feet  elevation 
will  be  gained  in  573  feet,  when  the 
slope  is  one  degree.  Where  the  slope 
is  two  degrees  the  10  feet  will  be  gained 
in  one-half  of  573  feet,  etc. 

3.  To  construct  a  scale  of  horizontal 
equivalents  all  we  have  to  do  is  to  first 
construct  a  scale  of  feet  for  the  map. 
Then  determine  our  vertical  interval, 
say  10  feet.  We  then  measure  off 
successively  on  a  line  a  map  distance 
of  573  feet;  this  is  the  horizontal 
equivalent  for  one  degree.  We  next 
measure  off  a  map  distance  of  287  feet. 


%• 


Night  Operations 


9 


and  this  is  the  horizontal  equivalent  for 
2  degrees  slope;  191  feet  for  a  3-de- 
gree  slope,  and  so  forth  up  to  the 
maximum  degree  of  slope  that  we  will 
encounter,  usually  10  degrees. 

4.  This  same  scale  of  horizontal  equiva- 
lents will  answer  for  a  map  with  a 
scale  of  3  inches  to  1  mile  with  a  ver- 
tical interval  of  20  feet;  6  inches  to  1 
mile  with  a  vertical  interval  of  10  feet. 

5.  The  scale  of  horizontal  equivalents 
printed  herewith  has  been  made  on  the 
principle  stated  above.  It  runs  from 
Yz  degre  to  10  degrees.     (See  Fig.  2.) 

Practical  Map  Reading 

Let  us  take  the  map  published  with  this 
article  and  systematically  read  it. 

2.  What  is  the  scale  of  the  map?  It  is  3 
inches  equal  1  mile  ;i  that  is,  3  inches  meas- 
ured in  any  direction  on  the  map  is  equal  to 
1  mile  on  the  ground.  Any  Ij^  inches  on 
the  map  will  represent  %  oi  a  mile  on  the 
ground.  We  see  that  there  is  a  representa- 
tive fraction  on  the  map.  This  is  only  an- 
other method  of  indicating  the  scale.  How 
has  it  been  determined?  Remembering  that 
a  representative  fraction  is  one  reduced  to 
unity  in  which  the  numerator  represents  the 
map  distance  and  the  denominator  the  ground 
distance  we  have: 

Map  Distance  3  inches 


Ground  Distance 
3  inches 


1  mile 
1 


63,360  inches       21,120 

This  may  also  be  expressed  1  :  21,120; 
that  is,  one  unit  of  measure  on  the  map 
represents  21,120  of  the  same  units  of  meas- 
ure on  the  ground, 

Q.  What  is  the  distance  from  the  railroad 
crossing   at    Goldenville    to    the   Boyd 
School   House   via   the   621-630-Stock 
Farm  road? 
A.  Measure  off  the  distance  along  the  edge 
of  a  slip  of  paper  and  apply  it  to  the 
graphical   scale   at  the   bottom   of   the 
map.    You  will  find  it  to  be  4,540  yards. 
Q.  How  long  will  it  take  a  company  of  in- 
fantry to  march  from  the  crossroads 
at  Hunterstown  to  a  railroad  crossing 
at  Goldenville?    The  company  marches 
at  the  rate  of  80  yards  per  minute. 
A.  By  measuring  the  distance  we  find  that 


it  is  8,230  yards.    The  company  march- 
ing at  the  rate  of  80  yards  per  minute 
would  consume  101  minutes  or  an  hour 
and  41  minutes. 
You  now  proceed  to  a  study  of  the  con- 
vential  signs  used  by  the  map  maker.    These 
conventional  signs  are  drawn  to  represent  as 
near  as  possible  the  feature  as  it  appears  on 
the    ground.      The    conventional    signs    em- 
ployed in  making  this  map  are  shown  below. 
Make  a  study  of  them  until  you  know  exactly 
what  every  mark  on  the  map  is  intended  to 
represent. 

CONVENTIONAL   SIGNS 


Impj-ovod  Roods 
Unimproved  Roads 
Trails 

Railnxids.Sirgla  Track 
"        Doubi^T^oo^< 
"       Urban  or  Suburban 
FeRces.E'arbod  VViro 

"      Smco+h  " 

■•      Worm 

"      S1"on3 

"      Medgg 
Streams  uncterl5'v/ide 

II        over     "      » 
Embonkmonf 
CuTtlrKj 
Arroyo  or  Ditch 

Buildings 
Bridges 
Stone  Culverts 


OHouse  a  Born 


'Corn 


Cultivated  ^ond 


Treesi  without  Underbrush 


Woods  with.  Underbrush 


Brush 


Pine  Trees  and -Rocks 


Orchard 


Morsh 


■i"     -r     J- 
■r      >r     r 


lu   a-      olo. 


o»->i' 


oooaoo  a 

ooaaaoo 

OOttOOOO 


All  blank  spaces  dre  Gross  Land 


mS^ldSfed  S'is^nT^'for^&mlon.'  Hunterstown  S-inch  map  as  the  map  given  here  has  been  very 


Night   Operations 


11 


You  observe  that  this  map  has  no  meridian 
on  it.  How  are  you  to  determine  directions  ? 
When  a  map  has  no  meridian  line  it  is  pretty 
safe  to  assume  that  the  reading  matter  runs 
from  west  to  east  and  that  the  up  and  down 
edges  of  the  map  run  north  and  south.  A 
hne  through  Fairview  School  House  and 
Goodintent  School  House  runs  north  and 
south.  This  line  would  serve  as  a  meridian 
for  work  in  the  center  of  the  map  and  the 
borders  for  meridian  lines  along  the  edges  of 
the  map.  You  observe  a  little  V-shaped 
affair  at  the  bottom  of  the  map.  The  line  to 
the  right  shows  the  true  north  and  the  one 
to  the  left  shows  the  magnetic  north ;  that 
is,  the  former,  if  the  map  were  oriented  on 
the  ground,  points  directly  to  the  north  pole 
and  the  latter  to  the  magnetic  north.  There 
are  comparatively  few  places  on  the  earth's 
surface  where  these  lines  coincide.  In  this 
case  the  magnetic  declination  is  7  degrees ; 
that  is,  if  you  were  to  take  a  bearing  with  a 
compass  there  would  be  a  variation  of  7 
degrees  from  the  true  north. 
Q.  What   is    the    direction    of   Hunterstown 

from  Fairview  School  House? 
A.  North  52  degrees  east.  This  is  deter- 
mined as  follows :  Draw  a  line  con- 
necting Fairview  School  House  with 
the  cross  roads  at  Hunterstown.  Draw 
another  line  connecting  Fairview  School 
House  and  Goodintent  School  House. 
This  latter  is  your  meridian  line.  Lay  a 
protractor  with  its  0-180  degree  edge 
along  the  meridian  with  the  center  at 
Fairview  School  House.  Read  along 
the  edge  of  the  protractor  to  the  point 
where  the  line  connecting  Fairview 
School  House  and  Hunterstown 
emerges  from  under  the  protractor. 
This  is  the  reading  of  the  direction. 
Q.  What  is  the  direction  of  Granite  Hill 
Station  from  Goodintent  School  House f 
A.  South  41  degrees  east.  Use  the  same 
meridian  line  and  pursue  the  same 
method  as  before  indicated. 
Q.  What  is  the  direction  of  Goldenville 
from  Hunterstown  Cross  Roads? 
What  is  the  direction  of  Boyd  School 
House  from  Goodintent  School  House? 
A.  Work  these  out  for  yourself. 

Note  the  Scale  of  Map  Distances  of  con- 
tour intervals.  Take  the  space  to  the  left 
of  the  scale  marked  1  degree.     This  means 


that  at  any  place  on  the  map  where  the  con- 
tours are  spaced  the  distances  apart  indicate 
that  the  ground  at  that  point  slopes  just  1 
degree.  Where  the  ground  is  steeper  the 
contours  are  spaced  close  together.  By 
keeping  this  scale  in  your  mind  you  can  tell 
by  observation  the  approximate  slope  of  the 
ground  at  any  point  on  the  map. 

Note  the  statement  below  the  scale,  V.  I.: 
20  feet.  This  means  that  the  vertical  dis- 
tance between  contours  is  20  feet.  So 
you  know  immediately  that  between  every 
two  contours,  no  matter  what  their  distance 
apart  may  be,  there  is  a  vertical  difference  of 
20  feet.  Suppose  the  map  had  no  such 
statement  on  it.  How  would  you  determine 
this  contour  or  vertical  interval?  By  an 
inspection  of  the  map.  You  will  observe  that 
the  contours  from  the  ridge  just  south  of 
Goldenville  are  numbered.  These  numbers 
indicate  that  the  vertical  interval  between 
contours  is  20  feet. 
Q.  What    is    the    elevation    of    the    Grubey 

House? 
A.  We  see  that  this  house  lies  about  midway 
between  the  580  and  600  contours;  the 
elevation  is,  therefore,  590  feet. 
Q.  What  is  the  difference  in  elevation   be- 
tween   the   McElheny   House  and    the 
Hamilton  House? 
A.  We  see  that  the  former  has  an  elevation 
of   540   feet  and  that  the  640  contour 
passes  through  the  latter.     The  differ- 
ence between  these  is  100  feet,  so  that 
the  Hamilton  House  is  100  feet  higher 
than  the  McElheny  House. 
Q.  Where  is  the  highest  point  on  the  map? 
A.  The  707-foot  hill  west  of  Goldenville. 
Q.  Where  is  the  lowest  point  on  the  map? 
A.  The    lowest   point    on    any    map   will    be 
found  at  the  point  where  the  largest 
body  of  running  water  leaves  the  map. 
This  "will  be   found   in   the   southwest 
sector  about   1,400  yards   southeast  of 
the  Boyd  School  House. 
In  order  to   facilitate  the  further  reading 
of    this   map    secure   a    10-cent   package   of 
"Crayolas"  and  proceed  as  follows : 

1.  With  the  blue  crayola  line  out  all  the 
stream  lines.  This  will  show  at  a  glance  all 
the  water  system  of  the  country  covered  by 
the  map. 

2.  With  the  red  crayola  line  out  the  560- 
foot  contour.  This  will  show  you  the  outline 
of    the    western    watershed    running    along 


12 


Night   Operations 


Oak  Ridge  and  its  extension  to  the  north ;  the 
watershed  immediately  west  of  the  main 
watercourse  and  that  to  the  east  in  the 
vicinity  of  Hunterstown. 

3.  With  your  green  crayola  line  the  500- 
foot  contour.  Make  note  of  its  crooks  and 
turns  which  indicate  the  shape  of  the  ground 
throughout  its  course,  then  compare  the 
green  line  with  the  red  line  indicating  the 
560  contour.  You  ought  from  this  process 
to  have  a  very  good  idea  of  the  country  cov- 
ered by  the  map. 

Tracing  out  the  water  system  of  the  coun- 
try included  in  the  map  we  find  that  the  main 
watercourse  runs  from  northeast  to  south- 
west practically  parallel  to  the  549-583-501- 
543-531  road.  Numerous  branches  lead  off 
to  the  east  and  west,  the  main  one  to  the 
east  crossing  the  above-mentioned  road  near 
501,  where  it  separates  into  two  branches, 
one  heading  in  the  high  ground  in  the  south- 
east sector  of  the  map  and  the  other  in  the 
high  ground  just  west  of  Hunterstown.  The 
main  branch  to  the  west  leaves  the  stream 
about  1,200  yards  due  west  of  543,  runs  in  a 
northwesterly  direction  to  a  point  700  yards 
southwest  of  the  Varney  place  and  then  turns 
northeast  and  runs  parallel  to  the  main  stream 
to  the  Hermon  place  and  forming  the  water- 
shed lying  between  the  two  streams.  An- 
other small  stream  leaves  the  main  stream 
and    heads    near    the    Boyd    School    House. 


Another  heads  near  the  C.  Topper  place  and 
runs  a  little  west  of  south,  forming  with  the 
main  stream  and  its  tributaries  the  water- 
shed designated  as  Oak  Ridge.  Another 
small  stream  heads  in  the  vicinity  of  Golden- 
ville  and  runs  southwest.  This  and  the 
branches  of  the  main  stream  form  the  water- 
shed which  lies  to  the  north  in  prolongation 
of  Oak  Ridge.  Over  in  the  northeast  sector 
of  the  map  there  is  an  independent  system 
of  watercourses  that  head  to  the  south  of 
and  in  the  vicinity  of  Hunterstown,  and  these 
with  the  branches  from  the  main  stream 
form  the  watershed  west  of  Hunterstown. 

With  your  colored  map  you  will  be  able  to 
pick  up  all  these  points.  The  study  should 
leave  you  with  a  good  mental  picture  of  the 
country  covered  by  the  map.  You  should  be 
able  to  approximate  distances  and  to  measure 
the  distance  from  one  point  to  another  with 
accuracy.  You  should  have  a  good  idea  of 
the  vegetation  covering  the  country  and  how 
it  would  look  from  any  point  on  the  map. 
You  should  have  knowledge  of  the  shape  of 
the  ground,  the  steepness  of  slopes,  etc. 
You  should  by  an  inspection  of  the  map  be 
able  to  solve  the  ordinary  visibility  problems 
that  may  come  up,  and  any  that  do  not 
admit  of  solution  by  inspection  should  be 
plotted  out  and  a  profile  of  sufficient  extent 
made. 


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